1. The resolution you input depends on how you're scaling your sprites, how you want your art to present, and what devices you're targeting. How that resolution is represented on screens that don't match the ratio of the resolution is controlled by the 'Fullscreen in browser' property. See this tutorial by Ashley for more:
https://www.scirra.com/tutorials/73/sup ... reen-sizes
2. This will depend on how you store your configuration options, how you control sessions, saving and loading, and so-on. Essentially, I would leave this concern for now - you can make your menu exactly how you want it, and it can be so isolated from the rest of the game as to be scrapped and re-written whenever you want. Construct 2 is a brilliant system for writing GUI.
3. I would use a 9-patch object to make the bubble itself, and a text object over the top to display the NPC's speech.